Background. An ideal reinforcing neo-sphincter should be innervated by the
pudendal nerve to work in coordination with the external anal sphincter. Th
e aim of this study was to create a skeletal muscle innervated by the puden
dal nerve without inducing external anal sphincter morbidity.
Methods, Seven dogs were used. On the right side of each dog, the distal en
d of thr transected nerve innervating the biceps femoris muscle was anastom
osed to the perineural window of the pudendal nerve, where the epineurium w
as excised over a small area without injuring the funiculus. Reinnervation
was studied 5 months after the operations. The left side of the dogs was us
ed as a control.
Results. For all 7 dogs, there was no macroscopic difference detected in th
e external anal sphincter: For 6 dogs, the biceps femoris muscle was preser
ved after end-to-side pudendal nerve anastomosis. After the pudendal nerve
central to the anastomosis site was electricallly stimulated, the external
anal sphincter contracted in all dogs. After end-to-side pudendal nerve ana
stomosis, the biceps femoris muscle contracted with the evoked potential in
5 dogs (71 %) and demonstrated electric activity at rest in 3 dogs (43 %)
but there was no reflex activity after anal stimulation. The ratio of type
1 to type 2 muscle fiber in the biceps femoris muscle after end-to-side pud
endal nerve anastomosis significantly changed and became the same as that i
n the external anal sphincter. The diameter of type type 2 muscle fibers in
the biceps femoris muscle significantly decreased after surgery. In additi
on, regenerated myelinated axons were observed in a cross section of the an
astomosed nerve in 6 dogs.
Conclusion. End-to-side pudendal nerve anastomosis is a promising technique
for the creation of an anal sphincter in patients who have fecal incontine
nce. The technique preserved the original external anal sphincter and creat
ed a skeletal muscle that was innervated by the pudendal nerve in 71 % of t
he dogs studied. This newly innervated skeletal muscle was capable of contr
acting in coordination with the original external anal sphincter on electri
c stimulation and also demonstrated characteristics closely similar to thos
e of the external anal sphincter.